OK, I see the issue. I had tested the code in the site's footer injection, not the header. This loads after the page content - including the prices. If it is in the header injection (in this case in the product's header), the code loads BEFORE the prices. If the prices aren't loaded, it can't change them. The code will need to be modified to check if the page is loaded first. I've amended the answer above so that you can use it in the header instead. I've tested this on Avenue to match your site.